The present invention relates to the art of functional neuromuscular stimulation. It finds particular application in providing hand control functions in central nervous system (CNS) disabilities such as quadraplegia and stroke victims and will be described with particular reference thereto. However, it is to be appreciated that the invention is also applicable to providing locomotive and control of other lower body functions in CNS disabled victims and to providing control of other muscles over which the patient has lost partial or full voluntary control.
In healthy humans, electrical signals originate in the brain and travel through the spinal cord and subsequently to peripheral nerves to a muscle which is to be contracted. More accurately, the signals travel to two or more muscles whose contractions apply forces antagonistically to a joint structure. The relative forces determine the degree and speed of movement. By appropriately applying the electrical stimulation to various muscles, a wide degree of voluntary movement can be achieved. In injuries to the CNS, the passage of electrical signals through the injured area may be disrupted. Commonly, lower spinal cord injuries will terminate the transmission of electrical control signals to muscles in the lower part of the body. Damage to the upper part of the spinal cord may block the flow of voluntary muscular control signals to upper and lower body regions. For example, in an upper spinal column injury at the C6 vertebrae, which is frequently injured in accident victims, muscular control below the elbows is commonly lost.
As early as 1791, Luigi Galvani produced artifical contractions in the muscle of frogs' legs by the application of electrical potentials. In the ensuing years, electrical stimulation therapy has been greatly refined. Cardiac pacemakers, for example, have become commonplace.
Several different groups of researchers have enabled paraplegic patients to stand and walk with walkers or crutches by applying preselected sequences to surface electrodes over their leg muscles. Surface stimulation is satisfactory for some walking and other less detailed movements. However, with surface electrodes, it is difficult to make an accurate selection of the muscle to be stimulated or an accurate prediction of the strength of the stimulus signal reaching the muscle.
Surgically implanted electrodes provide accurate selection of the muscle to be stimulated. Further, the stimulation remains more consistent over a long period of time. This renders implanted electrodes advantageous for the more delicate and complex motion associated with the hands.
Numerous experimental systems have been devised and implemented to provide computer controlled electrical stimulation to the muscles of the legs, arms, and hands of patients. These experimental systems are commonly large and bulky. Frequently, the patient must be connected with a personal computer or other small computer by a cable or tether. Although smaller, dedicated computer systems could be designed, the larger programmable computer systems are generally preferred for experimental flexibility. The response to a given stimulus varies widely among patients and over time within each patient. The larger programmable computer facilitates customizing for different patients and changes in a given patient.
The present invention provides a new and improved functional neuromuscular stimulation system which increases patient independence and performance.